What is a book? Spirit materialised in the form of a printed volume that celebrates the union of ink, lead and paper. But before it can become this extraordinary tool for transmitting thought, the book is first a project: the wager of an author grappling with their idea of the work to be written. The book in its nascent state is handwritten: it is loose sheets covered in crossings-out that record the formidable work of writing on writing by which the writer invents their text. This book on the book will therefore begin with these mysterious autograph adventures that tell the emergence of the text, from the very first scenario to its final version, via sketches, rough drafts, second thoughts, repentances, corrections, and up to the final typewritten “press-ready” text. To enter the secret laboratory of this creative process, we will follow, line by line, the genesis of one of Flaubert’s pages — the incipit of La légende de Saint-Julien l’hospitalier; it will be as if we were witnessing the book being written, hidden behind the writer’s shoulder as he works to blacken his large sheets of blue paper.